Some writers seem to swear by a notebook. Others swear at the mere suggestion of one.
Most artists make sketches. Most musicians will record something on their mobiles – probably.
Have some way of recording your thoughts, ideas, research, and inspirations, is essential.
Too much happens to us on any given day to remember every idea we have.
I think it was Under the Dome which Stephen King had the idea for when he was still a teacher. He may even have written a scene or section. That became something special when he eventually returned to it after becoming one of the most successful novelists of his generation.
Whether you use apps on your phone, or a notebook, or both, keep them handy and use them. Read back through them on a regular basis.
Transfer those ideas as you develop them to a bigger notebook or your laptop.
Return to them and with a little TLC they will grow into something special.